Warm-up control system for machine tool

ABSTRACT

A warm-up control system for a machine tool drives a spindle motor for rotating a main spindle of the machine tool before starting machining, thereby performing a warm-up operation, and acquires a spindle motor load value that is variable by heat generated during the warm-up operation. The warm-up operation is ended when the acquired spindle motor load value becomes substantially equal to a preset working reference load value. The cutting capacity of the main spindle can be improved by this warm-up operation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a warm-up control system for a machine tool.

2. Description of the Related Art

Conventionally, if a machine tool starts machining in a cold state, a shaft is thermally displaced so that the machining accuracy is degraded as the temperature of a spindle motor increases. Before starting actual machining, therefore, it is necessary to previously perform a warm-up operation by repeating a normal operation so that the machine temperature is stabilized, thereby maintaining temperature consistency.

A spindle motor controller for a machine tool is disclosed in Japanese Patent Application Laid-Open No. 2003-199378. This motor controller comprises an operation mode switching circuit for switching between a warm-up operation mode in which an warm-up operation is carried out and a normal operation mode in which a normal operation is carried out. In the case of the warm-up operation mode, the warm-up operation time is expected to be reduced by superimposingly applying high-harmonic voltage of a higher frequency than the drive frequency to a motor.

Various means have been devised to make the most of the cutting performance of a machine tool for cutting work. In general, a method is used to improve the cutting performance by increasing the mechanical rigidity, based on the machine design, main spindle design, and other factors.

In the warm-up control of the machine tool described above, the amount of thermal displacement of the machine tool, due to heat generation by rotational drive means, such as a motor, heat generation of a main spindle bearing, etc., is stabilized by idling a main spindle that is attached to the machine tool. This warm-up control, like the technique disclosed in Japanese Patent Application Laid-Open No. 2003-199378 described above, is used as a means for stabilizing the amount of thermal displacement of the machine tool due to the heat generation, and has never been used to improve the cutting capacity of the main spindle.

SUMMARY OF THE INVENTION

Accordingly, the object of the present invention is to provide a warm-up control system for a machine tool, capable of improving the machining capacity of the main spindle of the machine tool by a warm-up operation.

A warm-up control system for a machine tool according to the present invention comprises a warm-up operation executing unit configured to drive a spindle motor for rotating a main spindle of the machine tool before starting machining, thereby performing a warm-up operation, a spindle motor load value acquiring unit configured to acquire a spindle motor load value variable by heat generated during the warm-up operation of the warm-up operation executing unit, a comparison unit configured to compare the spindle motor load value acquired by the spindle motor load value acquiring unit with a preset working reference load value, and a warm-up operation ending unit configured to end the warm-up operation when it is determined as a result of the comparison by the comparison unit that the difference between the spindle motor load value and the preset working reference load value is within a predetermined range.

The warm-up operation may comprise acceleration and deceleration of the main spindle and steady-state rotation of the main spindle achieved by driving the spindle motor.

The spindle motor load value may be a value of current or a load meter value obtained from the spindle motor.

The warm-up control system may further comprise a reference load value setting unit capable of setting a plurality of the working reference load values and a reference load value selection unit configured to select one reference load value to be used for the comparison in the comparison unit, from among the reference load values set in the reference load value setting unit.

The warm-up control system may further comprise a warm-up operation end informing unit configured to inform of an end of the warm-up operation when the warm-up operation is ended by the warm-up operation ending unit.

The warm-up control system may further comprise a machining starting unit configured to automatically start the machining when the warm-up operation is ended by the warm-up operation ending unit.

According to the present invention, machining can be performed in a state where output of a main spindle is improved, by determining an end of a warm-up operation based on a spindle motor load value.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present invention will be obvious from the ensuing description of embodiments with reference to the accompanying drawings, in which:

FIG. 1 is a block diagram illustrating a principal part of a numerical controller for controlling a machine tool;

FIG. 2 is a graph illustrating an example of transition of a spindle motor load value during a warm-up operation;

FIG. 3 is a flowchart illustrating processing from the start to the end of the warm-up operation;

FIG. 4 is a flowchart illustrating processing after the end of the warm-up operation; and

FIG. 5 is a diagram illustrating set items for operating conditions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a block diagram showing a principal part of a numerical controller 10 for controlling a machine tool.

A processor (CPU) 11 of the numerical controller 10 reads system programs stored in a ROM 12 through a bus 21 and generally controls the numerical controller according to the system programs. A RAM 13 is loaded with temporary calculation data, display data, various data that are inputted by an operator through an LCD/MDI (manual data input) unit 70, etc.

An SRAM 14 is a nonvolatile memory that is backed up by a battery (not shown) such that it can maintain its memory state even after the numerical controller 10 is switched off. In the SRAM 14, a program for the measurement of an initial position, a program for thermal displacement correction of the machine tool, a machining program (described later) read through an interface 15, a machining program input through the LCD/MDI unit 70, etc are stored. Further, the ROM 12 is preloaded with various system programs for the execution of edit mode processing required for the creation and editing of the machining programs and processing for automatic operations.

The interface 15 is an interface for an external device which can be connected to the numerical controller 10 and is connected with an external device 72, such as an external storage device. The machining programs, thermal displacement measurement program, etc., are read from the external storage device. A programmable machine controller (PMC) 16 controls auxiliary devices or the like on the machine tool side according to sequential programs in the numerical controller 10. Specifically, necessary signals on the auxiliary device side are converted according to these sequential programs, based on M-, S-, and T-functions commanded by the machining programs. The converted signals are output to the auxiliary device side through an input-output unit 17. The auxiliary devices, e.g., various actuators, are activated by these output signals. When signals are received from various switches of a control panel on the main body of the machine tool, moreover, they are processed as required, and the result of the processing is delivered to the processor 11.

Image signals representative of the respective current positions of the individual axes of the machine tool, alarms, parameters, image data, etc., are transmitted to the LCD/MDI unit 70 and displayed on its display. The LCD/MDI unit 70 is a manual data input device provided with the display, a keyboard, etc. An interface 18 receives data from the keyboard of the LCD/MDI unit 70 and delivers it to the processor 11. An interface 19 is connected to a manual pulse generator 71. The manual pulse generator 71 is mounted on the control panel of the machine tool and used for precisely positioning of movable parts of the machine tool by respective-axes control with distributed pulses based on manual operation.

X- and Y-axis control circuits 30 and 31 for moving a table T of the machine tool and a Z-axis control circuit 32 receive move commands for the individual axes from the processor 11 and output the commands to servo amplifiers 40 to 42. On receiving these commands, the servo amplifiers 40 to 42 drive servomotors 50 to 52 for the individual axes of the machine tool, respectively. Position sensors are incorporated individually in the servomotors 50 to 52. Position signals from these position sensors are fed back as pulse trains.

A spindle control circuit 60 receives a spindle rotation command for the machine tool and outputs a spindle speed signal to a spindle amplifier 61. On receiving this spindle speed signal, the spindle amplifier 61 rotates a spindle motor 62 of the machine tool at a commanded rotational speed, thereby driving a tool. A position detector 63 is coupled to the spindle motor 62 by gears, a belt, or the like. The position detector 63 outputs feedback pulses in synchronism with the rotation of a main spindle, and the feedback pulses are read through an interface 20 by the processor 11. A clock circuit 65 is a clock device adjusted so as to synchronize with the current time.

It is experimentally confirmed that the value of the spindle motor load changes based on warm-up control by the numerical controller 10. In performing the warm-up control by the numerical controller 10 that drivingly controls the machine tool, the temperature of the spindle motor is also increased by a warm-up operation. As disclosed in Japanese Patent Application Laid-Open No. 2003-199378 mentioned above, therefore, the warm-up operation may possibly be controlled based on the spindle motor temperature. Since the spindle motor temperature is based on a plurality of temperature factors, such as the temperatures of a winding and rotor that influence the output of the spindle motor, however, whether or not the spindle motor output is improved cannot be determined based on the temperatures of the winding and rotor. Since a spindle motor load value is directly influenced by a spindle motor output, in contrast, the spindle motor output can be accurately determined. The value of current that flows through the spindle motor, acquired by the numerical controller 10, or a load meter value can be used as the spindle motor load value.

FIG. 2 is a graph illustrating an example of transition of the spindle motor load value during a warm-up operation.

As seen from the graph of FIG. 2, the spindle motor load value obtained when the spindle motor is in steady-state rotation (2) is lower than that obtained when the spindle motor is in steady-state rotation (1). Thus, the spindle motor load value measured during the steady-state rotation after the warm-up operation is lower than that measured during the steady-state rotation before the warm-up operation, which indicates that the spindle motor output is improved by the warm-up operation. Such improvement of output of a spindle motor is considered to be attributable to reduction of resistance due to increases of temperature of oil that lubricates friction spots inside the main spindle as well as to the characteristics of the motor used. The transition shown in FIG. 2 is only an example, and it may alternatively be shown in a different diagram depending on the characteristics of the spindle motor and the like. The spindle motor load value is given by the load meter value or the value of current flowing through the spindle motor acquired by the numerical controller 10.

The warm-up control according to the present invention will now be described with reference to FIGS. 3 to 5.

Before starting the warm-up operation, as shown in FIG. 5, necessary operating conditions for the warm-up control of the machine tool by the numerical controller 10 are manually set in the numerical controller 10. An operating condition setting 100 comprises a setting 110 used during the warm-up operation and an operation selection 120 after the end of the warm-up operation.

The setting 110 used during the warm-up operation comprises a setting 112 of one or a plurality of reference load values used to determine whether or not to end the warm-up operation and a setting 114 of a working reference load value (PmA) for selecting an actually used value, from among other reference load values set by the reference load value setting 112.

On the other hand, the operation selection 120 after the end of the warm-up operation comprises a setting 122 for automatic machining and a setting 126 for simply ending the warm-up operation. Further, the setting 122 for automatic machining comprises a setting 124 of the machining programs for machining, while the setting 126 for simply ending the warm-up operation comprises a setting 128 for informing an operator by means of audio-visual means, such as a lamp, buzzer, etc.

A spindle motor load value determined experimentally, empirically, or by calculation is set as a reference load value used to determine whether or not to end the warm-up operation (see reference numeral 112 in FIG. 5). A plurality of reference load values can be set, and that one of them which is to be actually used depends on the setting (see reference numeral 114 in FIG. 5) of the working reference load value (PmA). In a warm-up control system according to the present invention, the reference load value setting 112 of FIG. 5 corresponds to a reference load value setting unit capable of setting a plurality of working reference load values, while the setting 114 of the working reference load value (PmA) of FIG. 5 corresponds to a reference load value selection unit configured to select one reference load value to be used for comparison in a comparison unit, from among the reference load values set in the reference load value setting unit (112).

Warm-up control processing according to the present invention will now be described with reference to FIGS. 3 and 4.

[Step SA01] It is determined whether or not a warm-up operation mode is on. If this mode is on, the program proceeds to Step SA02. If not (NO), activation of the warm-up operation mode is awaited.

[Step SA02] The warm-up operation is started. Specifically, a program for performing the warm-up operation is read.

[Step SA03] The activity of the warm-up operation is read from the operating condition setting. [Step SA04] The spindle motor load value is acquired.

[Step SA05] It is determined whether or not a current spindle motor load value (D) is substantially equal to the working reference load value (PmA) determined by the operating condition setting. If the values are substantially equal (YES), the program proceeds to Step SA06. If not (NO), the program proceeds to Step SA07. If the difference between the two values is within a preset range, the values are regarded as being substantially equal.

[Step SA06] The warm-up operation is ended.

[Step SA07] It is determined whether or not a predetermined time (T) has elapsed. If the lapse of the predetermined time is confirmed, the program proceeds to Step SA04. If not (NO), the lapse of the predetermined time (T) is awaited.

[Step SA08] An operation to be performed after the end of the warm-up operation is selected. If the setting of the operation is the setting 122, the program proceeds to Step SA12. If the operation setting is the setting 126, the program proceeds to Step SA09.

[Step SA09] It is determined whether or not the setting 128 is selected. If the setting 128 is selected (YES), the program proceeds to Step SA10. If not (NO), the program proceeds to Step SA11.

[Step SA10] The operator is informed by audio-visual means, such as a lamp, buzzer, etc.

[Step SA11] The warm-up operation mode is turned off.

[Step SA12] The warm-up operation mode is turned off.

[Step SA13] Machining is automatically started. 

1. A warm-up control system for a machine tool, comprising: a warm-up operation executing unit configured to drive a spindle motor for rotating a main spindle of the machine tool before starting machining, thereby performing a warm-up operation; a spindle motor load value acquiring unit configured to acquire a spindle motor load value variable by heat generated during the warm-up operation of the warm-up operation executing unit; a comparison unit configured to compare the spindle motor load value acquired by the spindle motor load value acquiring unit with a preset working reference load value; and a warm-up operation ending unit configured to end the warm-up operation when it is determined as a result of the comparison by the comparison unit that the difference between the spindle motor load value and the preset working reference load value is within a predetermined range.
 2. The warm-up control system for a machine tool according to claim 1, wherein the warm-up operation comprises acceleration and deceleration of the main spindle and steady-state rotation of the main spindle achieved by driving the spindle motor.
 3. The warm-up control system for a machine tool according to claim 1, wherein the spindle motor load value is a value of current or a load meter value obtained from the spindle motor.
 4. The warm-up control system for a machine tool according to claim 1, further comprising a reference load value setting unit capable of setting a plurality of the working reference load values and a reference load value selection unit configured to select one reference load value to be used for the comparison in the comparison unit, from among the reference load values set in the reference load value setting unit.
 5. The warm-up control system for a machine tool according to claim 1, further comprising a warm-up operation end informing unit configured to inform of an end of the warm-up operation when the warm-up operation is ended by the warm-up operation ending unit.
 6. The warm-up control system for a machine tool according to claim 1, further comprising a machining starting unit configured to automatically start the machining when the warm-up operation is ended by the warm-up operation ending unit. 